1. Field of the Invention
This invention is related to an instrument for measuring trace constituents in the flow of exhaust from automotive engines. An instrument according to this invention is particularly well-suited for the measurement of engine oil consumption, as determined by the presence of combustion species attributable to chemical compounds contained in lubricating oil.
It is desirable for engine manufacturers to have a means for quickly determining engine oil consumption, because oil usage is important, not only for reasons of customer satisfaction, but also as a measure of basic engine integrity.
2. Disclosure Information
Many methods have been proposed for measurement of engine oil consumption. U.S. Pat. No. 3,473,372 to Klink discloses a system which uses a calibrated measuring vessel for determining oil usage. Such a system is hardly much of an improvement over the oldest known methods for measuring oil consumption in which the engine being tested was merely operated for an extended period of time sufficient to allow weighing or volume measurement techniques to determine, albeit with mediocre accuracy, the engine's oil consumption.
Engine designers have sought improved ways for measuring engine oil consumption for many years. One such alternative has involved the measurement of trace compounds in the engine exhaust. For example, a radiometric method involves the addition of a radioactive tracer to the oil, with the tracer being tracked in the engine's exhaust. This technique suffers from the drawback that it requires synthesis and addition of the radioisotope tagging compound, which renders the technique generally unsuitable for routine use.
Another method for determining engine oil usage involves the measurement of an oil additive, such as zinc dialkyldithiophosphate. Such a method is disclosed in U.S. Pat. No. 4,321,056 to Dimitroff. A sample of the exhaust gas in the engine is passed through a condenser in order to condense zinc sulphate in the exhaust. After the sample is treated, it is passed through a coulometer cell wherein a reading is obtained which is proportional to the engine oil consumed during the sampling period. This system, unfortunately, is incapable of giving a real time measurement of engine oil consumption.
Analytical systems for sampling exhaust gases for the purpose of determining the mass emission of various constituents have generally drawn the total exhaust flow through the system and combined the exhaust with make-up air so that the mass emission of a particular constituent could be determined notwithstanding that the mass flow through the engine being tested varied widely with time while the engine was being operated according to an unsteady cycle. U.S. Pat. No. 3,603,155 to Morris et al., U.S. Pat. No. 4,586,367 to Lewis, and U.S. Pat. No. 4,727,746 to Mikasa et al. all disclose systems in which all of the exhaust gases from a vehicular engine are drawn into the sample handling system of an analyzer. Such systems are undesirable from the standpoint that they require very large machines for handling and chilling the large volume of exhaust gases emanating from larger engines.
It is an advantage and object of the present invention that a system for measuring exhaust constituents according to this invention will operate by drawing into the machine only a small fraction in total exhaust flowing from the engine. As a result, the present instrument obviates the need for large air handling and chilling machines.
An instrument according to the present invention may beneficially use a coulometer as a detector for the exhaust constituent being measured. Electrochemical cells for measuring trace chemical constituents are disclosed in U.S. Pat. No. 3,928,162 to Takata, U.S. Pat. No. 4,029,563 to Binder et al., U.S. Pat. No. 4,409,069 to Luft and U.S. Pat. No. 4,622,105 to Liu et al. None of these cells is suitable for the continuous measurement of sulphur dioxide or any other trace element carried in the stream of exhaust coming from an engine, on a real time basis.
U.S. Pat. No. 4,277,368 to Amy et al. and U.S. Pat. No. 4,499,190 to Spicer et al. disclose coulometric and fluorescent techniques for detecting sulphur dioxide. As with the previously noted coulometric methods, these methods are not suitable for measuring sulphur dioxide in a flowing exhaust stream from an engine in real time because they lack adequate time response characteristics.
SAE Technical Paper Series 871913 entitled "Real-Time Measurement of Engine Oil Economy", which is hereby incorporated by reference in this disclosure, discloses a real time microcoulometric cell. The present invention uses a similar cell but also includes computer control for valves which operate various functions associated with the cell, as well as automatic introduction of electrolyte and calculation of the engine oil consumed by computer.
It is a further object of the present invention to provide an instrument using a coulometric cell powered by an electronic circuit which allows the cell to work in real time.
Other objects, features and advantages of an analyzer system according to the present invention will become apparent to the reader of this specification.